Wound condenser and method of producing same



NQVQ m 1942 H, KAPPELER 2,3013% WOUND CONDENSERS AND METHOD OF PRODUCINGSAME Filed May 15, 1940 Patented Nov. 10, 1942 UNITED WUUND CONDENSERAND METHOD OF PRODUCING SAME joint-stock company Application May 15,1940, Serial No. 335,348 In Switzerland August 12, 1939 (El. l'li -iifii M Claims.

This invention relates to wound condensers for high voltage purposes,and. is concerned with. the provision of an improved wound condenser,and with a method of forming the same. In particular, the invention hasspecific relation to socalled lead-through" (or lead in) insulators orcondenser iead-through devices.

Wound condensers for high voltage purposes consist of a wound upinsulation web into which. a metal layer is wound each time after a ceitaiu number of layers oi insulation. The length of the metal overlay isabout equal to the ctr-- once at the place concerned. in the same ad ininsulators are constructed with no radient control by means or; metalinso-calied condenser leaddn devices. eu found. that all hard paper condeosei iead through devioes,-consisting oi wound. up insulation webs andwounddn metal ioiis,-- assess such strong electric fields at the of thefoils, in operation with semi" nal voltage with ordinary stress of thedielectric of about it lav. cm, that the dielectric ad= jacent the edgesof metal foils does not re main constant but on the contrary isgradually affected. The result oi this is that the insulation isutilized electrically in a poorer manner, since it must be calculatedwith reference to the strong marginal fields therefore must he madethicker than would necessary other wise. The :iaot that small spacing ofadjacent metal inserts has favorable effect was known, it is true, butit heretofore was generally the practice to select spacings of from 2 toi mm. between. adjacent inserted metal layers, and in exceptional casesdown to 1.5 mm. The exact relationship between thickness of layer,voltage on the layer, and corrosion eilect of the edge was not knownprior to the present invention, and a thorough investigation making useof continuous experiments, a year long, was necessary for ascertainingthat relationship.

The present invention is predicated on the knowledge of the conditionsunder which one is in position to utilize the dielectric completelywithout edge corrosions occurring. It is based on the knowledge of thatvoltage under which no edge corrosion phenomena occur even with stresslasting for years. This limiting voltage has been found to be identicalwith that which can be ascertained by a simple experiment, the so-calledcorona discharge voltage, 1. e., that voltage at which,even assumingthat the edges of the layers are in the air,--a sound or an increase inlosses occurs for the first time upon increasing voltage. Since theedges of the conducting inserts are embedded in. soliddielectric-generally, in paper and artificial resin,--this discovery wassurprising. it shows that it must be assumed that the edges aresurrounded in the closest proximity with a iine air film of about normalpressure, although this cannot be determined with ordinary testingmethods.

The invention comprises making the thickness of dielectric betweenadjacent conducting layers so small, with a minimum stress of thevdielectric 01? iii 1 2v. per cm. that the volt ge oo cu between. thelayers in cuestio s not g eater than the corona discharge volta e corresponding to this thickness oi insulation.

it is true his recu meut spsces of any desired it electric strength oithe dielectric used eompleteiy,'i. e., if the condenser is @Vur.=dimen'sionet however, ne cording to the prose. '3 invention, theutilisation is complete, the otest radial spucing ja-cent ov rlaysremains uncles i. case. With very ei'ilcient dielectric, the spacingcan. frequently be the thickness a simple sheet of paper. it is thenpossible to moire wound high voltage condensers or insulators, and condenser lead-through devices, by constructing the overlays as strips ofconductive material in con tinuous sequence independent oi the diameterof the roll, the insulating distances from each other in the directionof the circumference necessarily being at least large enough so that theapper taming partial voltages do not lead to jumping.

In its product embodiment, the invention re sides in a wound condenser,for high voltage, of

the type including a continuous web of dielectric and conductiveoverlays separated into discern tinuous portions in. the direction oithe oircumierence of the wound device, e. g., hard pom! condenserlead-through devices, characterized in that with a minimum stress of thedielectric of 10 lav. per cm. with the highest permissible permanentnominal voltage the number of conductive overlays in the radialdirection is so large and, therefore, their radial spacing from eachother is so small that with said permanent nominal voltage betweenadjacent overlays the value of the corona discharge voltage is notattained.

It may be stated that the radial spacing of the conductive overlays ofthe wound condenser is not in excess of 1 mm.; that said overlays are inthe form of strips which are no wider (in the direction of thecircumference), and preferably are less wide, than the circumference ofthe roll diameter appertaining thereto; and that said the direction ofthe dielectric web and with so much relative insulating spacing betweenadjoining overlays that the same is at least sufficient for jump-proofabsorption of the drop in voltage between adjoining overlays. Thisspacing may amount to more, or less, than one circumference of the rollat the place of the spacing, depending upon the properties of theinvention and other variables. Thus, the spacing between two adjoiningoverlays may amount to one or two or more turns of the windings, or mayamount to only a fraction of one turn,

The boundaries of the overlay strips running crosswise of the dielectricweb may be parallel to the axis of the roll, or they may run in helicallines which form an angle of between 45 and 90 with the circumferentialline of the roll. Preferably, those boundaries of the overlay stripswhich run in the direction of the web are substantially parallel to theedges of the web. Moreover, the overlay strips may extend over theentire width of the dielectric web or over only a portion of the latter,and may or may not be uniform in area and/or dimensions from one pointin the roll to another; preferably, the lengths of the overlay strips(cross-wise of the web) progressively diminish from the center of theroll outwardly.

According to the invention, the thickness of the conductive overlaysdeposited on the insulation (dielectric) web amounts at most to athirtieth part of the thickness of the latter. The overlays consist atleast in part of carbon (e. g., graphite, lampblack, or the like) in avery finely subdivided,preferably colloidal"-form, and may contain alsovery finely subdivided metal.

The crux of the process embodiment of the invention resides in the stepof applying (1. e., depositing) the conductive overlays on the web ofdielectric itself as the latter is being wound up, the overlays soapplied being in such thin layers that their thickness is notperceptible in practice. Thus, the conductive overlay may be formed onthe dielectric web by applying spaced areas of conductive material onthe untreated side of an insulation web the opposite side of whichlatter has been coated and/ or impregnated with a resinous composition,e. g., shellac coating composition. For this purpose, the applying stepmay consist in spraying, printing or painting onto the insulation webspaced areas of a fluid composition comprising finely divided carbonwith or without added finely divided metal; or the applying step mayconsist in depositing a thin layer of the conductive material on theinsulation web by the aid of an electric field. The fluid carbonaceouscomposition may comprise an aqueous suspension of colloidal graphite (e.g., the products known in commerce under the notations Aquadag;Hydrokollag, etc.), or compositions similar to printers ink or to blackIndia ink.

In all cases wherein the overlay is applied to the insulation web byspraying (or printing, or painting) thereon a fluid compositioncomprising the conductive material of the eventual overlay, the liquidmedium is to be expelled from the coating layer before the web is woundup into a roll.

It is within the scope of the present invention to form the condenser orinsulator from a plurality of separate sheets of the insulation; also,to insert separate sheets (of insulating material) carrying theconductive overlays into the roll while winding up the continuous web ofdielectric;

in which case the latter may or may not itself carry conductiveoverlays.

The invention will be further described with reference to theaccompanying drawing, in which Fig. 1 is a perspective view illustratingschematically the method of forming the improved lead-through device ofthe invention;

Fig. 2 is an axial sectional elevation of a partially completedcondenser in accordance with one form of the article of the invention;and

Fig. 3 is an exaggerated, axial, sectional elevation of a completedcondenser in accordance with the invention.

Fig. 1 illustrates formation of a condenser. According to the same,overlays 9, with relative spacing a and with a width b smaller in thecircumferential direction than the circumference at that diameter of theroll, are applied on the paper web 2 to be wound up on mandrel I andcoated on one side with artificial resin solution. The length c of theoverlays in the direction of the axis can be limited at a distance dfrom the edge of the paper according to Fig. 1. The overlay could,however, be applied over the entire length in the direction of the axis,and the finished roll subsequently turned down conically, or in anothersuitable shape, approximately as in Fig. 3. This latter figure shows acondenser leadthrough device, in solid view below, and in lengthwisesection above, the turned down winding 4 being applied on thelead-through tube 21 and being encircled outside with the socket element22. In addition, the overlays can be allowed to increase or decrease intheir axial length according to any definite rule desired so that acondenser lead-through device according to Fig. 2 is the result, theouter shape of which is cylindrical. it is true, but whose controlinserts 9 become smaller from the inside towards the outside.

When, however, the conducting inserts are arranged in such small radialspacings, a number of practical diificulties are encountered. Both metalfoil sheets and metallized paper result in such considerable increase inthe radial thickness that the parts outside the overlays are under tooslight winding pressure. By equalizing papers that are allowed to run inbeside the layers only a partialcompensation of the thickness ispossible in practice and this complicates the process of manufacture toa practically impossible extent.

The invention, therefore, comprises a process of applying the conductinginserts on the insulation web of the wound condenser itself in such athin layer that their thickness is not perceptible in practice. This isthe case when their thickness amounts at most to 5 of the thickness ofthe insulation web. In practice this can be attained for instance byapplying carbon suspended in liquid on the insulation web after whichthe liquid is volatilized. The carbon is to be divided up as colloidallyas possible, in the form of lampblack or, even better, graphite. Asuitable suspension, for instance, can be obtained in trade under thenames of Aquadag," Hydrokollag," etc., but likewise certain types ofIndia inks and printing inks can be employde. The colloidal graphitesuspension can have the finest metal powder mixed with it. Theconducting layer can be sprayed, printed, or painted on the insulationweb, or applied thereto by an electric field. The liquid can be Water oranother suspension carrier.

I claim:

1. Wound condenser type bushing for high voltage, including a leadthrough conductor with conducting overlays divided up in the directionof the circumference of an insulation web and a mounting ring,especially hard paper-condenser leadthrough devices, distinguished bythe fact that with a minimum stress of the dielectric of kv. per cm.with the highest permissible permanent nominal voltage, the number ofoverlays in the radial direction is so large and therefore their radialspacing from each other so small that with said permanent nominalvoltage between adjacent overlays, the value of the corona dischargevoltage is not attained.

2. Wound condenser according to claim 1, distinguished by the fact thatthe greatest radial spacing of the conducting overlays of the rollamounts at most to 1 mm.

3. Wound condenser according to claim 1, in which the conductingoverlays are in the form of strips each of which is, at most, no widerin the direction of the circumference than the circumference of thecondenser at the locus of the strip.

4. Wound condenser according to claim 1, in which the conductingoverlays, are in the form of strips arranged, independent of thediameter of the condenser, in continuous sequence in the dircction ofthe circumference with so much relative insulating spacing betweenadjoining overlays that jump-proof absorption of the drop in voltagebetween adjoining overlays is assured.

5. Wound condenser according to claim 1, in which the conductingoverlays are in the form of strips whose boundaries, crosswise of theinsulation web, are substantially parallel to the axis of the condenser.

6. Wound condenser according to claim 1, in which the conductingoverlays are in the form of strips whose boundaries, crosswise or theinsulation web, run in a helical line forming an angle or from 45 to 90with the circumferential line of the roll.

'7. Wound condenser according to claim 1, in

which the conducting overlays are in the form of strips whoseboundaries, in the direction of the circumference, are spaced from theside edges of the insulation web.

8. Wound condenser according to claim 1, in

which the conducting overlays are in the form of strips whose lengths,measured in the direction of the axis of the roll, vary from a maximumnearest the center of the roll to a minimum nearest the periphery of theroll.

9. Wound condenser according to claim 1, in which the conductingoverlays are in the form of strips whose thickness amounts at most to athirtieth part of the thickness oi the insulation web.

10. Wound condenser according to claim 1, in which the conductingoverlays are in the form of strips whose composition comprises ilnelydivided carbon.

11. Wound condenser according to claim 1, in which the conductingoverlays are in the form of strips whose composition comprises finelydivided carbon and finely divided metal.

12. In the process of preparing a wound condenser including aninsulation web and spaced conductive overlays, the step which consistsin applying the conductive overlays on the insulation web itself, priorto the winding, inthe form of deposits or practically imperceptiblethickness.

13. Improved process defined by claim 12, in which the overlays aredeposited from a suspension of finely divided conductive material in aliquid medium.

14. Improved process defined by claim 12, in which the overlays aredeposited by spraying onto the insulation web an aqueous suspension ofconductive solids including a form of finely divided carbon.

' HANS KAPPELER.

